Micro-electromechanical systems (MEMS) and in particular resonators possess very high Q, and can be used to build oscillators, which makes them viable to serve as frequency reference devices (FIG. 1). Commonly, quartz crystals are used as a frequency reference. Such quartz is large and suffers from a low level of integration. MEMS oscillators are small, and can be integrated lowering cost significantly. However, MEMS resonators show a high sensitivity of frequency drift over temperature (e.g. +−5000 ppm over 100° C.), and are thus not as stable, as compared to a quartz crystal (e.g. +−1 ppm over 100° C.) (FIG. 2).
A MEMS resonator can be stabilized over temperature by sensing the temperature, and compensating the MEMS. Several solutions are provided in the prior art. Typically a micro-oven (3) is used to stabilize the temperature of the MEMS oscillator (4) (FIG. 3). A temperature sensor (5) in the oven measures the temperature which needs a high precision external temperature reference (6), and drives the oven temperature control (FIG. 3). In this way, the MEMS oscillator can be stabilized to e.g. +−20 ppm over whole ambient temperature range.
Temperature variations in the surrounding environment affect the interested properties of MEMS devices in an undesirable way. To cite an example, frequency of MEMS resonator is a function of its temperature which is influenced by the ambient temperature and heat flow. The micro-oven incorporates active heating/cooling elements to maintain the temperature of the MEMS device at desired value. Active cooling is not always necessary in which case the target MEMS temperature will always be above the surrounding temperature.
It has been found that the power consumption of such ovenized MEMS systems can be too high.